In history people have always been interested in methods and devices, be it mechanical, electronic or other, to automate the composing and/or playing of music. Especially since the so called MIDI-standard (Musical Instrument Digital Interface) was established in 1983 (MIDI 1.0 specification, Document No. MIDI-1.0, August 1983, International MIDI association), which defines a standard interface through which synthesizers, rhythm machines, computers, etc. can be linked together, substantial research has been devoted to the automated composing and/or playing of music.
Most of the resulting methods and devices were meant to automatically generate accompaniments to a solo instrument, to compose background music for films, plays and presentations or to produce music to entertain customers and to create the desired atmosphere in for instance restaurants or shops, commonly referred to as `elevator music` or `quiet music`.
One way of producing music automatically is to use an electronic system that produces so-called synthesized music. These systems generally comprise one or more electronic musical instruments or synthesizers and an automatic device producing control signals for them, which signals consist of digital code sequences in the case of this invention.
In the prior art methods and devices have been disclosed that use statistic approaches and employ for instance Markov processes, in which each musical note, fraction of a musical note or group of musical notes is treated as a single stochastic state in a sequence of states. Music is generated by probability functions stored in memory, starting from an initial musical code sequence (state) to which is added a successor code sequence having the highest probability according to the probability function. The Markov process is now in a new state and (part of) the increased sequence is used as a new initial code sequence so that the process endlessly generates control codes for one or more electronic musical devices that produce the resulting music accordingly. Additional rules are however necessary to produce typical musical structures and generate agreeable music. This method requires large amounts of training material to form the necessary conditional probability density functions in addition to the fact that synthesized music based on stochastic processes is usually quite monotonous.
Other prior art methods use heuristical rules based on musical expertise to produce such digital code sequences to control musical instruments. This technique is frequently employed in the field of artificial intelligence and is for instance disclosed in U.S. Pat. No. 4,926,737 issued to Minamitaka. The document U.S. Pat. No. 5,418,323 issued to Kohonen, discloses a method for controlling an electronic musical device that does not use heuristical rules, but forms a rulebase automatically on the basis of digital training sequences. The algorithm disclosed by Kohonen is based on finding a set of `grammatical` rules in a sequence of codes representing musical information. Kohonen uses so-called DEC (Dynamically Expanding Context) grammars, which were originally developed for on-line speech recognition. Human speech consists however of sentences that form grammatically well formed pieces of information of limited length, while musical `sentences` can be structures of undetermined length (e.g. long improvisations in Jazz). Because of this difference the rule base will haves to be updated very frequently during the training phase.
The construction of the rulebase from training material can either be static, i.e. based on the input and (batch)processing of existing (previously recorded) code sequences representing musical information, or dynamic, i.e. based on real-time input of codes by an electronic musical device, for instance an electronic musical instrument. The Kohonen algorithm is reasonably efficient in the case of input and batch processing of existing training sequences but, given the current performance of PC hardware and software, inefficient to use for real-time improvisation, because of the necessary frequent updates of the rule base.
The present invention avoids or alleviates certain problems and drawbacks associated with the prior art some of which are mentioned above.